CLINICAL SYMPTOMS OF SCHIZOPHRENIA AFFECT REFERENCE-INDEPENDENT MEASURES OF TASK-INDUCED EEG ALPHA-ASYMMETRY

Differential patterns of EEG alpha asymmetry during verbal and spatial cognitive activity are commonly described and are thought to reflect predominance of left- vs. right-sided cortical activation. Although th ese patterns have been difficult to elicit reliably in schizophrenics, the, authors have previously suggested that clinical status may have confounded results. Therefore, EEG data from 17 additional schizophren ic patients, 16 mood disorder patient controls, and 17 normal controls were used to examine the relationship between severity of schizophren ic symptoms and task induced alpha asymmetry. Subjects performed verba l and spatial tasks during recording of 16-channel EEG. After transfor mation to the average reference, log alpha power from central and temp oral leads was analyzed by MANOVA and MANCOVA. The expected task-side interaction (P < 0.02) was present for the total sample and for each c ontrol group when analyzed alone. However, it was only present in schi zophrenics when the BPRS score was entered as a covariable. Patterns o f correlations between BPRS scores, left temporal alpha power, right/l eft temporal alpha ratios, and task differences in ratios suggested th at higher symptom levels were associated with excessive left-sided act ivation during spatial activity. This is consistent with other evidenc e of left hemisphere overactivity in schizophrenics. (C) 1997 Elsevier Science Ireland Ltd.